Landracing Forum
Tech Information => Steering - Suspension - Rear End => Topic started by: mitchell968 on April 15, 2012, 09:01:43 PM
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after searchin the archives here a bunch , and a little on the hamb , i need some advice on chosing a gm 7.5 in rear end for my g/str , and i have a question for the roadster guys about body widths and rear axle track widths ect. i bought 32 frame rails from vhr , frame will be completed by them later this year and im wanting to put a 29 polyform on it but cant find rear bodywitdh dimensions and havent contacted polyform on it yet , but im thinking my rear axle should in the 56 in neighborhood as far as an outer drum to drum width ? hambers say a 3in wheel off set looks proper and will keep the tires close to the fenders ?,is this right ? is that good for bville ? how close does that leave me between the body and tire with goodyear 28s ? and for the rear end guys(thanks tony) , what years and models of gm 7.5 2 series would fit this kinda low buck , low tech, low hp build ? im hoping sparky will chime in on this , you seem to be the resident 7.5 guru. i'll start a build thread after i get the completed frame from vhr some time after sw this year. meanwhile , please feel free to fill in any blanks in my questions here . its a great feelin for me to finally be purchasing parts and getting this project going in , well , some direction . dont forget your double smileys. thanks for your help. mitchell
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Hi Mitch.
Are you sure a G roadster is gonna pull 3.08's?.....the series 2 is 3.08 down to 2.14:1....that's a lot for a G motor, how fast you think you'll go? Depending on what kind of bullet you're planning on 28's and a 3.08 will give you about 26mph per 1000rpm, where does your motor make it's power? where does it redline? whats the current record in the class? Aim to have the motor at peak power at the current record speed in top gear.....then calculate the rear end ratio you need to achieve this.
I should have kept me gob shut but you can convert one way or the other, I think it's 2 to 3 with a spacer, Sparky will tell us...
I am a fellow sufferer, but half a world away..... we'll be running Ford 28 spline axles into a Torsen centre in a 7.5. If you can choose your width it's a lot easier, you've got a bit of work ahead of you......but I'm sure you'll love it.... :wink:
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Mitchell, your first issue is to be sure your body will be legal for STR. The roadsters have a lot of rules, including more body measurements than NASCAR. Search the site, there have been a couple of body measurment charts posted.
Work backwards from motor info to figure out your gearing. We usually try to gear the lakester for the speed required just below the HP peak RPM. You can make adjustments with tire sizes.
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Don't forget to take into account the tire growth. On a LSR 28" Good Year you can have much as 1" growth and about 1/2" on the sidewall. Tony
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Tony --
We're nat'sass on the money with 28" Goodyear drag tires. We figure tire growth cancels slippage. Come within a mile an hour squinting at the Isky dream wheel.
Probly got around 700 ponies and took some real changes to get much over 200 with 3.10s with our '29. But, then again, a real one isn't as slick as a Polyform (flush doors, almost no coupe' pillar, no hinges, no gas cap, etc.).
Got to be a heck of an Unblown G motor to do that.
Stan
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records 132.6 licensing and learning car
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4.11:1 x 6500rpm x 28's = 127mph :cheers:
x7000rpm =136.8mph
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that helps . thanks
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found 4.10s 2000lbs , 133 mph needs 367 hp. is that weight realistic ? 300 + hp from 122 c.i. not difficult
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found 4.10s 2000lbs , 133 mph needs 367 hp. is that weight realistic ? 300 + hp from 122 c.i. not difficult
May I ask how you came up with 367 HP needed to go 133 mph in a 2000 lb. STR? You might want to recalculate. Is this for Bonneville, El Mirage, Ohio Mile, Loring, or the Texas Mile?
Tom G.
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calculator on a formula site . got a good one ? bville only. is that a realistic weight !?
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So, it seems like a doable thing. Having said that welcome to the world of LSR . Now is your chance to lie awake at night wondering what the car that set the record was like, how they got their power, what weight the car was , how long did it take for them to get that speed out of it?.... there aren't many records that are an easy get, some look easy.....
there was recently a story ( the link was posted by Mike)about one of the ol faves of landracing.com Jack Dolan and his challengers in a S2000 Honda....
http://www.caranddriver.com/features/not-so-fast-there-bud
it gives a great insight into this game............
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been losin sleep over it for 3 yrs. only able to really get started recently. sw 2010-11. 2012 will be the last w/o a car. with enough help, that is.
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calculator on a formula site . got a good one ? bville only. is that a realistic weight !?
Something is not calculating that is for sure, here is my old setup. My STR I have for sale in the Classifieds, with a 355 Chevy that had a 3/4 hydraulic race cam, 600 cfm Holley, early Chevy FI heads, weighted 2500 lbs., Quick change Rear end, Automatic Trans, and never ran over 5700 RPM ran a best of 163 mph, at El Mirage. If the motor I had in the car put out 1 HP per CU, I would be amazed. Body is a 29 Ford Roadster.
Hope this helps.
Tom G.
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it does. thanks. ballpark #s are what i need to get on track here. . i ordered a hot rod calc.
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Mitchell--When we ran our Quad 4 powered Comp Coupe a number of years ago, our combo was worth about 260-270 hp on alchohol. We started with a 5speed 240z trans, never could pull 5th gear, even with the 3.70 rear gear we had. Switched to a Muncie 4 speed. That worked pretty well--got us a 166mph record. By the way, we used a Monza Rear end with 8inch Ford Axles and Axle Ends....That Monza unit is sort of a 7.5GM unit....doesn`t take much horsepower to drive it either.
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good stuff , thanks paul. i have emails sent to mr eyres and poly form on the 29 body measurements and legality of poly forms pieces, and to several engine builders to see what we can do with some of the 4 cyls.
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Go the Muncie, easy to shorten them, the 10 bolt is a good choice because the pinion is close to the centre of the crown wheel making them v efficient like the Monza.
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Something is not calculating that is for sure, here is my old setup. My STR I have for sale in the Classifieds, with a 355 Chevy that had a 3/4 hydraulic race cam, 600 cfm Holley, early Chevy FI heads, weighted 2500 lbs., Quick change Rear end, Automatic Trans, and never ran over 5700 RPM ran a best of 163 mph, at El Mirage. If the motor I had in the car put out 1 HP per CU, I would be amazed. Body is a 29 Ford Roadster.
Hope this helps.
Tom G.
Mitchell.... are you stuck on building this thing from scratch? reread this post if you are open to making an existing car work for you. It may need a few updates for head restraint, and a little work to get a 2 liter shoehorned in where a V8 lived... :roll: but as was mentioned to another on the site, this car is cheap, can be made runable this year and based on the numbers easily capable of setting the record with your 300 HP 2 liter. You will be well over $20K, maybe even $25K, getting to the point this car is if you do all your own work without hiring anything out. Do some math and soul searching, the roadster class is one of the toughest to build to and compete in on the salt (read pass tech in impound). Tom's car would get you there this year.
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Dr. Goggles --
No need to shorten the trans. in Street Roadster. I think you tanked with that advice.
Stan
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stainless , im very bent on building from the ground up , minus my vhr frame , for a million reasons. one being, im now a workin stiff , no more "fishing boat" money. low budget build. i was figuring on closer to 35 K so thanks for the encouragement. im enjoying the process , havent had much to do with any fast stuff since my boat racing days. thank you sir. mitchell
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Mitchell, if you're planning on going to a N/A 4 banger, the best place to go shopping is in the USAC midget world. Out dated spare engines (to them) are plentiful & good bang for the buck. Lots of midget action in your neck of the woods too.
Sid.
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thanks sid , i checked out the wmra site and am gonna talk to some of the folks at skagit, and the roush zetec would work fine for a licensing car. i spied it a while back. transend in auburn wa is going to build my 7.5 for a 29 when i get to that point .thanks again . mitchell
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I you want to be competetive why not 21s on the rear
17 dragsters on the front or some more 21"
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21 inch tires is what im gonna run sparky , 29 is refering to the mike cook body im gonna build for. and thank you sir. mitchell
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wait a minute . mr back tells me to run 22s 0n the front , others are saying 28s on the rear, so if have 21s on the rear im gonna look my dirt bike. i need more help on this. thanks mitchell
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d-r-a-g-
2.14s with 21" X 8000=234
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I think I was talking you down from something bigger with the 22s. What's the weight rating of the 17" dragster tires, Sparky? 234 would be an impressive number for a G/StR.
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Stan, That was just to show what was possible 2.28 or 2.41 would most likely fit a G I sure do not think a G would pull 2.14 s with out HELP lol
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like HELP with a B / and a / F ?
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No F in StR.
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nothing gets past you guys.
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Question when it comes to the HP you all are mentioning. WHen you say x hp, are you talking at the flywheel or at the rear wheels? Desoto man mentioned the motor in his str not making one hp per cu and yet it ran pretty well at el mo. My 394 SBC that I had in my dragster made 625 at the flywheel. Just makes me curious what a similar motor would run in a 2600 lb str such as Desotos. Obviously that would fall in the B category and at the small end of the range so it wouldnt be knocking on the door of any records. Not trying to hijack the thread Mitch, was just reading along and wasnt sure how you all were figurung hp.
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M968 as others on the list will testify---I am not very concerend about how things look---lol
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Question when it comes to the HP you all are mentioning. WHen you say x hp, are you talking at the flywheel or at the rear wheels? Desoto man mentioned the motor in his str not making one hp per cu and yet it ran pretty well at el mo. My 394 SBC that I had in my dragster made 625 at the flywheel. Just makes me curious what a similar motor would run in a 2600 lb str such as Desotos. Obviously that would fall in the B category and at the small end of the range so it wouldnt be knocking on the door of any records. Not trying to hijack the thread Mitch, was just reading along and wasnt sure how you all were figurung hp.
Frankie,
Lets just say my motor made one HP per inch at the flywheel (350hp), with your motor it should go approx 197 in my car.
Tom G.
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Frankie,
Lets just say my motor made one HP per inch at the flywheel (350hp), with your motor it should go approx 197 in my car.
Tom G.
Tom, I meant to say more than one HP per inch not less sorry, wasnt trying to knock the motor you had. Its good to know what a motor like I had would do in a STR if I decide to go that route. Is that approx 197 at El Mo or the salt?
Frankie
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Tom, I meant to say more than one HP per inch not less sorry, wasnt trying to knock the motor you had. Its good to know what a motor like I had would do in a STR if I decide to go that route. Is that approx 197 at El Mo or the salt?
Frankie
Frankie,
Don't worry about it, my motor was a piece of junk, cast crank, stock rods, two bolt mains, etc. Just wanted to see what I could do with it. El Mirage is the answer to your question.
Tom G.
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Howdy,
have a technical question to ask about running the 7.5in 10-bolt rear at Bonneville. I'm still waiting on my rule book but going off of the checklist in the rookie guide, I need positively retained axles. What is the common/recommended way to do this on the 7.5in 10-bolt? I saw Ford 8in axles and ends listed, is this a cheaper way than the more common 9in housing ends and custom axles?
Thanks,
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look weird---go fast---put the smallest tires you can that fit the rules---cant go below15" wheels
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look weird---go fast---put the smallest tires you can that fit the rules---cant go below15" wheels
Not sure I'm following you there, though it is good to know I can't run the stock 14in wheels. Need to find some 15in steelies.
I thought it would be best to run taller tires to compensate for less than optimal gear availability and the fact the engine I'm planning on using won't rpm over 6000rpm.
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he was in roadster minimum 15" wheels the little GM 7.5 has the greatest selection of ratios for LSR you are going to have to put C-clip eliminators in any way!! change!!!
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he was in roadster minimum 15" wheels the little GM 7.5 has the greatest selection of ratios for LSR you are going to have to put C-clip eliminators in any way!! change!!!
Do ya'll tend to use the bolt on ones that go on the housing ends and use the stock axles or are you talking a full blown housing end change with new axles and a Ford 8/9in bearing?
My appologies for the hijack off of the orginal question but I thought it was best to put it in the same thread since it's titled with the axle itself.
Thanks,
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he was in roadster minimum 15" wheels
"The minimum wheel diameter for all Vintage Category vehicles with the exception of / VOT is 14 in ". - page 54, 2012 rule book - Tony
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Thanks for the catch Tony
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GM 7.5" fact corrections:
Ratios mass-produced:
2.294:1, 2.412:1, 2.5625:1, 2.733:1, 2.929:1, 3.077:1, 3.231:1, 3.417:1, 3.727:1, aftermarket 3.909:1, 4.10:1, 4.30:1, 4.556:1
There were a few aftermarket 3.546:1 sets. Happy hunting for those.
HP capacity: around 500, fully built. Forget a 900-horse anything unless there's NO traction. In which case why have 900 horses?
With stock 28-spline axles, or aftermarket 26-spline axles, the weak link is typically the R&P, even with a girdle, though I've failed the differential cross pin, behind a 170-horse 305 with an automatic transmission. May have been a defective pin.
'85-up were 7.625" ring gear, possibly excepting S-10 / Astro, which easily fits all 7.5" cases. 28-spline shafts appeared in Camaro / Firebird, even V6/auto, in mid '89 or mid '90, I forget which. Probably '90.
S-10 starts narrowest overall, '93-'02 'maro / 'bird is widest. All '82-'02 'maro / 'bird versions used a torque arm, all Malibu / Monte / Cutlass / Regal / Grand Prix used a triangulated 4-link, all others were leaf springs.
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You missed one, the highest ratio is a 2.136.
Sid.
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GM 7.5" fact corrections:
Ratios mass-produced:
2.294:1, 2.412:1, 2.5625:1, 2.733:1, 2.929:1, 3.077:1, 3.231:1, 3.417:1, 3.727:1, aftermarket 3.909:1, 4.10:1, 4.30:1, 4.556:1
There were a few aftermarket 3.546:1 sets. Happy hunting for those.
HP capacity: around 500, fully built. Forget a 900-horse anything unless there's NO traction. In which case why have 900 horses?
With stock 28-spline axles, or aftermarket 26-spline axles, the weak link is typically the R&P, even with a girdle, though I've failed the differential cross pin, behind a 170-horse 305 with an automatic transmission. May have been a defective pin.
'85-up were 7.625" ring gear, possibly excepting S-10 / Astro, which easily fits all 7.5" cases. 28-spline shafts appeared in Camaro / Firebird, even V6/auto, in mid '89 or mid '90, I forget which. Probably '90.
S-10 starts narrowest overall, '93-'02 'maro / 'bird is widest. All '82-'02 'maro / 'bird versions used a torque arm, all Malibu / Monte / Cutlass / Regal / Grand Prix used a triangulated 4-link, all others were leaf springs.
I have (2) Monza rears, one 2.29:1 and one 3.08. Can I swap those gears into my 3.42:1 1987 Camaro rear? I've read where the S-10 gears can be swapped into the Monza rear if you machine the pinion. Reading the above quoted post makes me think the Camaro rear used the smaller parts until 89, and the "machined" S-10 gears were 85 and up. Also, the 500 HP noted above, is that a general rule, or 'asphalt' limit, and the 900 HP a 'salt' limit, or ???? My engine makes 690.
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I run a AA/GL with this rear with 2.14 ratio, The pinion is HUGE and a pretty good 565 BBC about 9.5 on the hp--with no problems
BUT: I run no torque converter, and a PG/GV set up---My guess would be that one can run 2X that much hp ---so long as one stays away from SHOCK LOADS ymmv
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...... Can I swap those gears into my 3.42:1 1987 Camaro rear?
Your Camaro should be the 7.5 or the 7.625 and the gears will work with one problem if that is what you have. They need a 2 series carrier and with the 3.42 you have the 3 series carrier. So the housing would be ok, but you need to get the 2 series open carrier or torsen (recommended) if you go to those gears. You can find them on e-bay if you keep looking. If you go with the torsen center you will also go from 26 spline to 28 spline axles but the 28 spline are as large as you can go. The torsen...
http://www.torsen.com/products/T-2.htm (http://www.torsen.com/products/T-2.htm)
.... also comes in a 2 and 3 series so get the correct one. The flange where the ring gear fits is thinner on the 2 series to get the correct spacing for the larger pinion. You can go from a 2 series to a 3 series gear set by buying a spacer to go on the carrier but not the other way. Torsens came in some Camaro's from about '99 to 2002 or in that neighborhood (the info is out there).
Here is a link to a place that has a 1350 yoke for the 7.5 rear-end...
http://www.dennysdriveshaft.com/p1056_1350_series_pinion_yoke_for_7.5_inch_10_bolt_with_27_splines.html (http://www.dennysdriveshaft.com/p1056_1350_series_pinion_yoke_for_7.5_inch_10_bolt_with_27_splines.html)
... they are hard to find. Good luck,
Sum
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The Motor Vehicle Manufacturing Association files don't show the 2.14:1 for anything, ever, so that's why I specified mass-produced. I may stand corrected. But if so, that would have to be a 47:22 ring and pinion, which is a huge jump from 2.29:1 and 2.41:1 both using a 17-tooth pinion. 37:17 would be 2.17647:1 which seems more plausible. Otherwise the teeth would be microscopic, but you'd likely always have at least part of at least 2 pinion teeth pushing on the ring gear.
500 HP is the practical upper limit for street, beyond 500 it's a ticking time bomb, guaranteed to fail sooner or sooner. Even if you buy every upgrade and avoid both drag radials and shock loads. On salt it may not matter, I have no experience yet.
I'm not sure the Torsen that was factory optional in 4th-generation Z28s, Formulas and Trans Ams was used with the 2.73:1 gears standard with an automatic. Those used Auburns, which I have many good experiences with. The optional gear for automatics was 3.23:1, and 6-speed manuals got 3.42:1 only, except '93. I'm sure '93 was Auburn-only, but there was a deep-geared T56 for 2.73:1, and another T56 for 3.23:1. I'm sure the Torsen required the optional ratio for automatics. I know for fact my '95 Z28 auto was 2.73:1 Auburn, right from GM. The Auburn was so driveable in dry, wet, snow, dirt, and gravel, that I'd expect it to be excellent on salt. Even with more than 100,000 miles on one, twin black stripes were easy, even on dry pavement. Auburns do wear out, and are difficult to freshen.
I've heard that the Monza was different from all other 7.5s. Non-Monza 7.5" gears fit 7.625" housings, obviously, and generally the reverse is true with no clearancing. ANY 7.625" R&P WILL fail before you need a 1350 yoke.
From my own experiences and from all I've read on LS1Tech.com, I would run a girdle, but I would not run much preload. Richmond gears are the strongest, but also the loudest.
Nobody ever discusses lubes versus backlash versus torque capacity, let alone stress-relieving by vibration, or cryo-treating, but I had a 3.73:1 7.5" survive 470-ish HP on drag radials, 3600# race weight and automatic transmission, running 80W90 non-synthetic and no girdle.
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The Motor Vehicle Manufacturing Association files don't show the 2.14:1 for anything, ever, so that's why I specified mass-produced. I may stand corrected. But if so, that would have to be a 47:22 ring and pinion, which is a huge jump from 2.29:1 and 2.41:1 both using a 17-tooth pinion. 37:17 would be 2.17647:1 which seems more plausible. Otherwise the teeth would be microscopic, but you'd likely always have at least part of at least 2 pinion teeth pushing on the ring gear.....
You know a lot more about GM rearends than I do, but the 2.14's are pretty easy to find along with the 2.28/2.29's. I bought the last set these guys had, but it was a new gear set (look at top of page)....
http://www.tomsdifferentials.com/2011catalog/Pages35-37.pdf (http://www.tomsdifferentials.com/2011catalog/Pages35-37.pdf)
Used sets come up on ebay fairly often. We have a used set we got from John on here and Sparky has a few sets himself.
On the torsen they were in some of the '98-02 Camaro's/Firebirds and in the 2 series and 3 series (we need the 2 series)....
I have a Torsen differential that starts with the numbers 9032 or 9022. Which differential is it? Top of the Page
Those numbers are Torsen part numbers associated with the production 7.6" GM F-Car series (Camaro, Firebird) vehicles. The 9030, 9031 and 9032 numbers refer to the low numeric series or Series 2 axles (2.73, 2.93, and 3.08 rear axle ratios) whereas the 9020, 9021, and 9022 numbers reference the high numeric or Series 3 axles (3.23, 3.42, 3.73, and 4.11 rear axle ratios).
http://www.torsen.com/general/general_faq.htm#Is%20it%20true%20that%20the%20Torsen%20unit%20in%20the%20production%20Camaro%20needs%20the%20GM%20modifier%20added (http://www.torsen.com/general/general_faq.htm#Is%20it%20true%20that%20the%20Torsen%20unit%20in%20the%20production%20Camaro%20needs%20the%20GM%20modifier%20added)
I bought one off of ebay and Buddy gave us another one in a Camaro rearend. There is a 2 series listed now...
http://www.ebay.com/itm/98-02-Camaro-7-5-2-73-Differential-Ring-Pinion-POSI-10-bolt-28-spline-Torsen-2/121298075478?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222008%26algo%3DSIC.MOTORS%26ao%3D1%26asc%3D21399%26meid%3D5853243939430586486%26pid%3D100011%26prg%3D9407%26rk%3D1%26rkt%3D10%26sd%3D310845086559
I agree that 500 might be the upper limit on the street but I know of at least one 900+ HP car that has run the 2.14's and a torsen without breaking them. Remember that the salt only has about 1/2 the traction as pavement and these cars don't make hundreds of runs,
Sumner
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Okay, I'll stop disputing what I don't have personal knowledge of. Sorry. :cheers: